refoam?

Agree the time to replace all of the foam surrounds is when one of them tears.
Different products have vastly different lifespans, so no way to predict when yours will go. ozone, hard use, sunlight, all play a part.
So you could be wasting money replacing perfectly good surrounds!

I don't believe foam surrounds go bad in one day. They are degrading gradually over time and yours are about due. If you want to know how your speakers are supposed to sound do a little preventative maintenance and have the surrounds professionally replaced now.

I agree with Rrog. I don't think that it happens overnight, and they are pretty old. Great speakers...have them done right.

Just a little true story: I found a pair of early 1970's JBLs in a second hand store for $30 the pair. The surrounds were shot. So we used little cut bits of duct tape (cut into trapezoidal shape) and used then to make a so-so duct tape surround. (trying to emulate the 'roll' in a real surround) That was many years ago. She still uses those JBLs as is, with the duct tape surround. With her $30 Marantz 2270....
This is cheap Hi fi. the real thing.
(no real connection to the op question, just a fun comment)